Many devices have been proposed to assist the motorist of a vehicle in avoiding collisions. One area of the art can be considered proximity detectors which rely on the amplitude of a received signal to indicate that a certain minimum distance has been established. These devices require that the lead automobile and the following automobile possess the same equipment. These devices generally utilize an auxiliary emitter and receiver to indicate the relative distance between a lead automobile and a following automobile. Devices of this nature rely on amplitude of the transmitted waves to trigger a warning system on a following automobile. For example, a lead car emits light waves and when a following car encounters these waves, an alarm is triggered to indicate to the following motorist that she or he is in close proximity to the lead car. A representative patent in this field is U.S Pat. No. 3,892,483 issued to Saufferer on Jul. 1, 1975. Saufferer discloses a distance warning device for vehicles. His invention concerns the rearward transmission of waves so that a following vehicle would receive the waves and either indicate that the following vehicle was too close, or automatically brake the following vehicle to avoid a collision. Saufferer relies on wave detection or monitoring of wave amplitude as the means for determining distance between the two vehicles.
Another area of the art can be considered distance measuring devices that rely on the Doppler effect. These devices are autonomous--they do not require that another vehicle have a compatible system. These devices generally utilize a wave emitting and receiving component located on the primary vehicle. By emitting wave energy and analyzing the reflected wave, an approximation as to distance between the primary vehicle and another object can be determined. When a certain minimum value corresponding to a minimum safe distance is reached, the motorist of the primary vehicle is alerted or his or her vehicle is caused to slow in response thereto. A representative patent in this field is U.S. Pat. No. 4,833,469 issued to David on May 23, 1989. David discloses a proximity sensing system that uses the Doppler principal to warn a motorist of a vehicle that he or she is approaching an object at an unsafe speed. This is accomplished by comparing the relative speeds of the vehicle to the measured object.
Both of these systems, the proximity detectors and the distance/velocity devices using the Doppler principal, look only to the vehicle directly in front of or behind the motorist. These systems are designed to warn a motorist that an unsafe condition may exist, based upon distance considerations. These systems are reactive and not proactive i.e., these systems warn a motorist only after a hazardous situation has been encountered.
Under many circumstances, knowledge of the condition of a vehicle directly in front of a motorist is adequate. That, of course, is the purpose of brake lights and turn signals. However, as the nations' highways become more and more congested, more and more "chains" are formed. These chains, a term used from the common phrase "chain reaction", occur when a linear progression of vehicles closely follow one another. It is in these situations that accidents are very likely to occur--especially when driving conditions are poor such as during a snow storm or in dense fog. For example, from 1981 to 1989 783 people died on California highways because of fog related accidents. Clearly, many of these accidents could have been avoided if each motorist in the chain of vehicles knew of the preceding vehicle's actions without relying upon significantly impaired, external visual cues.
Often, a motorist immediately observing the brake lights of a preceding vehicle does not realize his or her minimum stopping distance may be greater than that of the preceding vehicle. Or even more common, a preceding vehicle can see a hazardous condition and be prepared to respond; however, those motorists following this vehicle are shielded from that critical information and must only rely on the brake lights of the preceding vehicle to inform them of forth coming adverse conditions. This problem is best exemplified where a tractor and trailer truck obstructs a motorist's view of conditions in front of the truck. For example, if the brakes of a vehicle in front of the truck are applied, the motorist following the truck must wait for the truck to apply its brakes, change lanes, or otherwise become aware of the condition that requires braking or avoidance.
In chains, the delay from motorist to motorist in responding to brake lights of the vehicle in front of him or her becomes significant. On the average, it takes 0.25 seconds for the human brain to observe and analyze a condition, and an additional 0.25 seconds for a corresponding reaction to the observation to occur. Consequently, each motorist in a chain of vehicles imparts an average of a 0.5 second delay in response to the system. In a five automobile chain, the last motorist will observe a brake light on the preceding vehicle no sooner than two full seconds after the situation has manifested. However, if the last motorist in a chain was able to determine whether or not any preceding motorist, other than the immediately preceding motorist, in the chain was braking, then that motorist could ANTICIPATE braking, thus he or she could begin decelerating prior to observing a traditional indication that there was a need to brake.
During adverse driving conditions, a reaction delay is even more undesirable. The above described situations assume that a motorist's perceptions are not impaired. However, in adverse driving conditions such as bad weather, smoke, or dust, etc., a motorist's ability to perceive hazards is significantly reduced. Further, a motorist's ability to observe the condition of a preceding vehicle is also impaired. In addition, road conditions may cause the effective braking distance of a vehicle to be significantly greater than when traveling during favorable road conditions. The ability to anticipate hazardous conditions by receiving information not subject to human reaction delays and not subject to visibility limitations would significantly decrease the occurrences of chain reaction type, multiple vehicle collisions and injuries.
Therefore, there is a need for a distant early warning system for use by motorists and the like to provide information to such operators about actions and conditions occurring in front of them. Information such as whether or not preceding vehicles in a chain of vehicles are decelerating would permit a motorist to prepare to avoid hazardous conditions that could damage property or injure persons.